Treasurer Joe Hockey wants his extraordinary increase in the nation’s credit limit to half a trillion dollars to be approved by both house of Parliament this week.

But in a surprise move, the Labor opposition plans to turn the tables on the once debt-averse Mr Hockey and will move an amendment to halve the proposed increase by $100 billion, taking the limit to $400 billion rather than $500 billion.

Mr Hockey told his party-room meeting in Canberra on the eve of the first sitting of Parliament in the Abbott era that the debt ceiling was the second thing to be introduced after the repeal of the carbon tax and must be dealt with immediately.

He said amendment of the Commonwealth Inscribed Stock Amendment Bill needed to pass through both houses by Thursday, as the Senate does not sit next week.

At the first Coalition joint party meeting since the election, Prime Minister Tony Abbott warned MPs to maintain the discipline they had displayed during the opposition years, saying unity and collegiality were vital.

The Liberal Party’s federal director, Brian Loughnane, also addressed the meeting telling MPs their success did not change the country’s concerns over economic security, adding that people were sick of »Canberra games».

The opposition’s decision to check the amount of allowable borrowings is likely to see the Greens deciding the limit because they have the balance of power in the Senate.

Shadow treasurer Chris Bowen said Parliament should not be called on to lift the credit limit without supporting information on the current state of the budget.

»The only publicly available budget estimates would support an increase of the limit to $400 billion,» he said.

»The Treasurer has refused to release MYEFO — his mini-budget — which would track any estimated increases in peak net debt.

»Australians aren’t able to get new mortgages or credit cards without submitting their personal financial information for scrutiny, so it’s a bit rich for Mr Hockey to take the public credit card to half a trillion dollars without updated budget estimates.

»The only reason the Treasurer has put on the table for the 66 per cent increase in the debt limit is that it would be politically inconvenient to have to come back to the Parliament again. That’s just not good enough.»

In his comments to Labor’s caucus, Opposition Leader Bill Shorten said Labor MPs should not underestimate the task ahead of them, describing it as »immense».

He, too, stressed the need for discipline.

»As we start the 44th Parliament our party is united — and we’ll be all the stronger for it,» he told them.

»We will take the fight up to Tony Abbott and this government — and in this room we have the best team to do that.»